Magnetic resonance imaging (MRI) is a noninvasive way to take pictures of the body.

Unlike x-rays and computed tomographic (CT) scans, which use radiation, MRI uses powerful magnets and radio waves. The MRI scanner contains the magnet. The magnetic field produced by an MRI is about 10 thousand times greater than the earth's.

The magnetic field forces hydrogen atoms in the body to line up in a certain way (similar to how the needle on a compass moves when you hold it near a magnet). When radio waves are sent toward the lined-up hydrogen atoms, they bounce back, and a computer records the signal. Different types of tissues send back different signals.

Single MRI images are called slices. The images can be stored on a computer or printed on film. One exam produces dozens or sometimes hundreds of images.

For more information, see the specific MRI topics:

• Abdominal MRI
• Chest MRI
• Cranial MRI
• Heart MRI
• Lumbosacral spine MRI
• Spine MRI